Originally Posted by Fou-Lu
Have you followed the documentation here: http://php.ca/manual/en/mysqli.installation.php?
Looks like you're on windows, so you'll need to add the libmysql.dll to a system path if you have < 5.3. 5.3+ won't need the libmysql.dll, so I'd suggest updating the PHP version anyway if you are < 5.3. If not, check the httpd logs, it should be triggering an error if you've uncommented the extensions in PHP but it still won't load.
Windows 7 Home Premium
Apache 2.0.64 (Newest Windows version I found)
PHP 5.2.17 (to be compatible with live server)
MySQL 5.5.29 (oddly enough the phpinfo()) script doesn't even mention MySQL)..
The installation tutorial(s) I used were all found on the same site (which of coarse I can't recall now).